Condenser



March 1927 J. B. DEMPSTER CONDENSER Filed Dec. 14, 1922 w a j PatentedMar. 22 1927.

PATENT OFFICE.

JAMES B. DEMPSTER, OF IOWA CITY, IOWA.

coiaDENsER.

Application filed December 14, 1922.

My invention has to do with certain electrical condensers of the airinsulated type. It is the object of my invention to provide a variablecondenser of the type under consideration of simple, durable andinexpensive construction.

Another object of my invention is to provide/such a condenser, having aseries of fixed plates and a. series of movable plates, so constructedand mounted that when the movable plates are moved to position foroverlapping the fixed plates, the capacity of the condenser will bevaried according to the square of the angular displacement of theplates.

Aparticular object is to provide a condenser, having plates of suchshape and so mounted as to permit the movement of the plates to positionwhere the capacity is substantially zero.

A further object is to provide such a condenser having a series of fixedand a series of movable plates, in which the movableplates may beoperated with a rotary movement.

Another object is to provide such a condenser having plates of suchshape as to permit the building of the condenser to occupy a minimumspace, so that. it may be compact and thus convenient for storage,transportation and installation.

An additional object is to provide such a conden er having the parts soconstructed and arranged as to give the condenser sufficient sturdinessor strength to insure the proper spacing of the movable plates withrelation to the fixed plates during the operation of the condenser. Y

A further object is to provide a condenser of the type underconsideration, which is peculiarly adapted foruse in radio telegraphyand telephony equipment.

With these and other objects in view, my invention consists in theconstruction, ar-

' rangement and combination of the various parts of my device. wherebvthe objects contemplated are attained, as hereinafter more fully setforth, pointed out in my claims, and

illustrated in the accompanying drawings, in which:

Figure 1 shows a front elevation of a com- Serial No. 606,898.

plete condenser installed on an instrument board.

Figure 2 shows a rear elevation of the same with the movable Vernierplate in raised position.

Figure 3 shows a. side elevation of the installed condenser with all themovable plates in their positions of minimum capacity.

Figure 4 shows a vertical, longitudinal, sectional view taken on theline 44 of Figure 1.

Figure 5' shows a transverse, detail, sectional view taken on the line5-5 of Figure 3.

Figure 6 shows an enlarged, fragmentary top or plan view of a portion ofthe condenser; and

Figure 7 is a diagrammatic view illustrating a fixed and a movableplate, illustrating the various elements which are involved in adetermination of the size and shape of the plates.

For convenience, I have shown the condenser installed upon an instrumentboard or panel or the like, which in the accompanying drawings, I haveindicated by the reference character 10.

My condenser is of the type employing a number or series of fixed platesand a numher or series of movable plates adapted to be moved to variouspositions overlapping portions of the fixed plates.

In the accompanying drawings, I have disclosed a supporting frame,comprising the spaced end frame members 11 and 12 and an intermediatesimilar frame member 13. The frame members 11, 12 and 18 have projectingears or the like 14, 15, 16 and 17.

The ears 14 of the various frame members mentioned are arranged inalignment with each other, and similarly the ears 15 are aligned, theears 16 are aligned, and the ears 17 are aligned.

A rod 18 is extended through the ears 14 and has nuts 19 on the oppositesides of the ears 14.

A rod 20 is extended through and supports the ears 15 and also has nuts19, similar to those already described, for holding the frame members11, 12 and 13 properly spaced and rigidly supported.

A rod 21 is similarly extended through the ears 16.

It will be understood that the parts jus described form a rigidframe-work.

Extended through the ears 17 is a rod 22. The rod 22 is insulated fromthe frame memher 13 by means of a sleeve or the like 23 formed on thewasher 24. On the rear end of the rod 22, I preferably mount a nut 22.

On what may be called the forward; end of the rod 22, a head 25 of hardrubber or other suitable insulating material is detachably mounted bymeans of a set screw or the like 26. Mounted on the rod 22 is a sleeve27, which terminates short of the forward end of the rod 22, as shown inFigure 4, and has mounted on its forward end a suitable dial or the like28.

The sleeve 27 terminates at its'rear end just rearwardly of the framemember 12, as shown in Figure 4. The sleeve 27 is insulated from themembers 11 and 12 by means of sleeves 29 and 30 formed on washers 31 and32.

The rod 22 and sleeve 27 are mounted to rotate freely with relation tothe supports in which they are arranged and with relation to each other.

Supported on the frame formed by the parts hereinbefore described andpreferably on the rods 20 and 21 is the series of fixed condenserplates. These plates are indicated on the drawing by the referencecharacter 33. The peculiar shape of the plates will be hereinafter moreparticularly referred to, since therein lies one of the most importantfeatures of my invention.

The plates 33 are spaced from each other equidistantly on the rods 20and 21 by means of spacer sleeves 34. For two of the spacer sleeves 34on the rod 21, I substitute insulating sleeves or washers 35 of greaterdiameter than the sleeves 34 for the purpose of engaging the movablecondenser plates, as hereinafter more fully explained.

A series of movable condenser plates 35 is arranged to coaotwith theplates 33. The bodies of the plates 35 and 33 are preferably of the sameshape.

The plates 33 have ears 36 and 37 which project from the bodies of saidplates and are mounted on the rods 20 and 21. The plates 35 have ears38, which are mounted on the sleeve 27.

The ears 38 of the plates 35 are held equidistantly spaced apart fromeach other on the sleeve 27 by means of the spacer sleeves or washers39, which are similar in construction to the washers or sleeves 34.

The parts are so arranged that when the sleeve 22 is rotated a certaindistance in each direction two of the plates 35 engage the insulationwashers 35 for limiting the rotation in one direction or in the otherdirection, as the case may be. (See Figure 6.)

The rotation of the sleeve 27 and the consequent movement of the plates35 is accomplished by means of the dial 28.

The principal features of my invention are illustrated in theconstruction already described with the addition of some minorconducting parts, but for a commercial condenser,I use also what issometimes called the Vernier attachment.

On the rod 20 between the frame members 12 and 13 and spaced therefromand from each other, I place a pair of plates 33, similar in form andarrangement generally to the plates 33, and on the rod 22 between theframe members 12 and 13 and spaced therefrom and arranged in a planebetween the planes in which the plates 33 lie, is a plate 35*, similarin general construction to the plates 35. A flexible wire 39 isconnected with the rod 18. On the frame member 13 is' a binding post 40,with which is connected 2. wire 41. A connecting strip 42' extends fromthe post 40 to the post 43 and thence to the rod 22. The posts 40 and 43are insulated from the frame by sleeves 40".

In order to insure absolute certainty 01 contact and electricalconnection between the post 40 and the rod 22, there may be employed forconnecting these two elements a. flexible wire 44.

It will be noted that the plates 35 may ferred to is used for securingeven more accurate results with the condenser.

The plate 42 is of spring metal. The post 43 has a nut 45 on its rearend for permitting some adjustment, and the spring plate 42 thus servesto keep the rod 22 pressed to the limit of its forward movement.

On the frame member 12, another plate 42, similar in construction to theplate 42 is mounted in a manner similar to that of the plate 42. Theplate 42 at its upper end engages the rear end of the sleeve 2'7 forpressing it towards its forward end.

In this connection, it will be noted that the condenser plates areadjustable by means of the nuts on the rods on which they are mounted,and that the spring plates 42 and 42 are slightly adjustable.

This makes possible the arrangementof the fixed and movable condenserplates, so that they will never contact during their overlappingmovement.

111 any resonant electrical circuit, it: is desirable to have a variablecondenser.

In the usual practice, there is employed an inductance'coil and acondenser.

1n the so-called inductance coils commonly employed, the inductance isvaried by steps. This is accomplished by connecting or disconnecting acertain number of turns of the wire of the coil for each step.

Experiment and demonstration have shown that it is desirable in acondenser used with such an inductance device to be able to vary thecapacity according to the square of the angle of displacement of theplates of the a variation of the wave-lengths to which the equipmentwill respond. The wave-lengths to which the equipment will respondvaries directly according to the number of steps throughout the range ofthe inductance.

It therefore follows that the condenser should be so constructed thatwhen the movable plates are moved to overlapping position with relationto the fixed plates, the capacity should increase according to thesquare of the angular displacement.

From the standpoint of practical commercial construction, it isdesirable to have a condenser made with two series of plates, in whichthe plates of the respective series have pivotal movement with relationto each other. Such a construction makes for convenience in operationand convenience in installation of the condenser on 'a panel orinstrument board, and for compactness and strength of structure.

I have found that I have had considerable difiiculty in ascertaining theproper shape for the plates of the condenser, which would permit thepreferred construction and mounting above explained and which would besuch that when the plates of the respective series were entirelydisengaged, the capacity of the condenser would be approximately zero.

In Figure 7 is shown a plate 01, which may be one of a fixed series, anda plate 0, which may be one of a movable series. The plate a ispivoted'to rotate about the point e causing it to overlap the plate d.The shape of the plates shown in Figure 7 is such that the capacity ofthe condenser built with such plates varies according to the square ofthe angular displacement of the plates, when the movable series isactuated to overlap the fixed series.

It will be understood that my invention involves a structure in whicheither or both of the \series of plates are movable to rotate on apivot, but for purposes of illustration, I have preferred to show a.fixed series and a movable series of plates.

I will now outline a method for determining the shapes of the condenserplates of the kind shown herein, which plates are illustrative of a formin which my invention may be embodied and a method of arriving at thetheoretical outlines of such plates.

In the form shown, the plates 0 and d are made exactly alike with theexception of allowances made for the tongues or arms for mounting themovable plates on their pivots and the stationary plates on theirsupports.

It is understood that for purposes of practical construction, the actualplates must vary somewhat in outline from the outline of theoreticallyperfect plates.

The right and left halves of the plate (5 as divided on the line f gpassing through the pivot point e are exactly similar except that theone-half is the reverse of the other. For our purpose then, we needconsider only that portion of the plate 0 bounded by f k e f, so that jis any point on the outer curve f k and Z any point on the inner curveit 6. Then 6 j equals R and e Z equals 1*, and the angle a e 7' equalsP. If the angle P is given in radian measure then R equals plus m iWhere m is a constant, then; the

Either of these relations being satisfied, then calling S the areabounded by ll Z j it, then it follows that S equals P where k is aconstant.

If we assume that the capacity varies as the overlapping area of theplates, then (3" (capacity) varies as S and equals 7:: P or the capacityvaries directly as the square of the angle of displacement, and sincethe wave-length varies, as the square root of the capacity, then thewave-length will be directly as the angle of displacement, which is theresult desired.

In the foregoing, I have considered only one plate, to-wit, the plate aof Figure 7, but it is obvious that if the plates 0 and d are of similaroutline and are .nade to overlap, by moving the plate 0 on its pivot,then the overlapping area of the plates 0 and (5 will be twice thatconsidered in the foregoing explanation of one plate, and the capacitywill still vary directly as the .square of the angle and the wave-len thas before. varies directly as the angle.

In laying out the curves, f j h and e Z it (Figure 7) in the manner justde- /1- plus m P;

P being any angle through which any radius is drawn, m a constant, 1"the length of the radius from e to Z and R the length of the radius fromc to j.

With equal facility, I may assume an outer curve f j h and lay ofi.theinner of both d (stationary plate) -(movableplate), and that cretains the curve 6 Z k and obtain the values of r from the equation 1'equals or any portions of either curve may be arbitrarily selectedandlaid oif and the corresponding portions of the other curveconstructed by the use of the proper one of the above formulae.

It is desirable to give to the plates a shape, such that when themovable plate does not at any point overlap the fixed plate, thecapacity of the plates or condenser will be approximately zero. Toaccomplish this purpose, it is desirable in selecting a curve to startwith, to select such a curve as will bring an apex h somewhere in theradius e a; that, isto say, the selection of a curve terminating at h inthe line 6 a will give to the half plate an apex at-h' and thus give tothe plate such a shape that when the movable plate and the fixed plateare in the osition, illustrated for instance in Figure the plates willhave substantially zero capacity In order to facilitate the"construction of a condenser having approximately zero capacity incertain relative positions of the different series of plates, and alsofor securing practical commercial advantages in the structure of thecondenesr, it is desirable to make the stationary and movable plates ofsubstantially the same outlines, as for instance illustrated in'Figure7, although from the foregoing equations, it'follows that one plate mayhave any shape, providing that a e coincides with e j which is a radiusoutline given from the foregoing equations,

andproviding that the outlines of 0 are such that the remaining parts ofthis plate completely cover 0 when 0 is in the position of highestcapacity.

It thus follows that the plates of a condenser of the kind underconsideration may be made with theoretically perfect shapes, asillustrated in Figure 7 It will be understood that in Figure 7, I haveshown a theoretically perfect plate. .The plates shown in Figure 5 forinstance illustrate the plate actually used in my condensels, which arecorrect according to the above formulae except that the have theprojecting ears for mounting t em in the complete device.

It is obvious that the shapes of the plates may, vary from the perfectand still come within the spirit and purpose of-my invention, wherebyplates are made of the proper outlines and are convenient for mountingin a device, which is compact, simple and cheap, andwhich'has its partssuitable for operation by a dial. This device is convenient for theordinary panel or instrument board.

I claim as my invention:

1. In a condenser, fixed plates, coacting pivoted similar plates eachhaving each half thereof outlined by two dissimilar curves,

the radius of one of said curves at any point therein equaling thesquare root of the sum of the square of the radius of the other curve toa point in the same radius plus the product of a constant times theangle through which the radius is drawn, thus:

substantially as shown and described.

2. In a condenser, a plurality of fixed plates and a plurality ofcoacting pivoted plates adapted to be moved to position overlapping withrelation to the fixed plates, the overlapping portions of theplates'.being outlined by dissimilar curves produced according to theformula in which the radius of one curve equals the square root of thesum of the square of the radius of the other curve to a point in thesame radius and the product of a constant times the angle through whichthe radius is drawn, thus:

Des Moines, Iowa, December. 4, 1922.

JAMES B. DEMPSTER.

